I. Field of the Invention
The present invention relates generally to heat-treated, bent laminated glass products, including bent, laminated, fully-tempered or heat-strengthened glass panels for use as enhanced safety glazing material in architectural and interior applications, and a method of manufacturing them. More particularly, the invention relates to veneered, fully-tempered or heat-strengthened glass panels comprising an alkali-aluminosilicate, glass layer cold-bent over a polymer interlayer to form a protective barrier that safely encapsulates the internal residual stresses, which, in the event of its breakage, prevents particles from dislodging and subsequent disintegration. Relevant prior art can be found in USPC 65 (i.e., “ . . . glass processing . . . ”), Subclasses 25.4, 104, 106 and others; and USPC 428 (i.e., “ . . . stock materials . . . ”), Subclasses 195.1, 410-411, 421, 426-438, and 442-444.
II. Description of the Prior Art
As is well recognized in the art, there are a wide variety of bent glass products, involving both heat-treated and non-heat-treated products. Bent glass is flat glass which has been shaped while hot into a body having curved surfaces. Typically, bent glass products are distinguished by a variety of factors and characteristics. The flat glass sheets which are hot bent are typically of a “soda-lime silicate” composition available in raw sheets of exceptional quality and flatness as made by primary producers with the “float process” known in the art. These raw sheets are usually clear, ultra clear low-iron, or they may be tinted gray, bronze, green, or blue. They may have a coating applied by the primary producer to yield special properties such as water-damage resistance, scratch resistance, or low-emissivity and/or reflectance. Heat-treated bent glass typically refers to a flat, glass sheet which has been not only heated to temperatures of about 620 degrees C. and above, then bent in its hot plastic state, but also force cooled to impart a compression/tension relationship between its surfaces and core.
There are two principal kinds of heat-treated glass: “heat-strengthened” and “fully-tempered” glass. Heat-strengthened glass is cooled slower than fully-tempered glass, which is cooled faster and exhibits relatively higher surface compression and corresponding internal tension. Heat-treated, fully-tempered, bent glass is characterized as having a surface compressive stress of at least 69 MPa., or an edge compressive stress of at least 67 MPa., and deep residual stresses that, if released in the event of breakage, result in a self-propagating fracture pattern into small, but sometimes clumped, dull particles. Fully-tempered glass with appropriate testing may be classified as a safety glass product in the United States of America suitable for many architectural and interior applications. Heat-treated, heat-strengthened glass, as defined broadly, is characterized as having a surface compressive stress of at least 24 MPa. Heat-treated, heat-strengthened glass, as defined more narrowly by industry standard ASTM C1048, is characterized as having a surface compressive stress of between 24 MPa. and 52 MPa. Heat-strengthened glass has deep residual stresses that, if released, also cause a self-propagating fracture pattern but into larger pieces. Without secondary lamination, heat-strengthened glass is not classified as a safety glass because its fracture pattern includes larger particles. Heat-treated bent glass has relatively fast rates of production, owing to the quick cycle of heating, bending, and rapid cooling.
Non-heat-treated bent glass refers to annealed glass, with or without later chemical-strengthening, which has also been heated to temperatures of about 620 degrees C. and then bent in its hot plastic state, but which is cooled slower than “heat-treated” bent glass to prevent the buildup of residual stresses within the glass. Non-heat-treated, annealed, glass has minimal surface compressive stress, typically not more than 1.38 MPa., and is characterized as being without strength enhancement but internally stable. Annealed glass without secondary lamination is not classified as a safety glass product because its fracture pattern includes large, sharded particles. Non-heat-treated, chemically-strengthened glass is annealed glass which, following cooling, has been subject to an ion-exchange process to impart the surface region with a high level of compressive stress by chemical means, and thus enhanced strength. The compression forces, while typically at a level on the surface far higher than fully-tempered glass, extend to only a shallow depth measured in microns. The corresponding tension stress, the same forces which cause fully-tempered glass to disintegrate into small particles, are distributed across the remaining thickness at a lower level insufficient to result in a granular fracture pattern except on very thin sheets. Chemically-strengthened glass without secondary lamination is not classified as a safety glass because of this typically larger fracture pattern. Non-heat-treated, bent glass has slow rates of production with long cycles of heating, bending, and cooling, plus multiple secondary hours in a salt tank, if chemically-strengthened properties are required.
Heat-treated glass must be made as individual pieces because of the need to force cool all glass surfaces simultaneously to uniformly impart compression/tension forces. Typically, optical quality and edge quality are both excellent, as each heat-treated glass piece is produced as a single monolithic panel. A highly polished edge finish may be added before bending, and remains unchanged by the heat-treating process. Compressive stresses in the surface of glass sheets are desirable because microscopic flaws are forced closed allowing higher thermal or mechanical loads including impacts to be tolerated before a flaw opens and a crack propagates into breakage. Compressive stresses within heat-treated, fully-tempered glass provide enhanced strength which is at least four times the strength of annealed, bent glass of the same thickness Compressive stresses within heat-treated, heat-strengthened glass provide enhanced strength which is at least two times the strength of annealed, bent glass of the same thickness. However, the shape conformance is less accurate than non-heat-treated bent glass, because the deep residual stresses always slightly alter the shape with some level of unpredictability.
Once the glass is heat-treated, excessive thermal or mechanical loads including by impact may result in breakage with the release of internal residual stress and subsequent disintegration, explosively in the case of fully-tempered glass. However there always remains a risk of such failure occurring spontaneously even years after production due to imperfections in the glass. For example, the presence of microscopic inclusions of nickel-sulfide contaminant in raw flat glass sheets which increase in size over time is a well documented cause of spontaneous breakage. Additionally, damage or dimensional changes to the glass edges or surfaces after heat-treating instead of causing immediate breakage may result in instability causing spontaneous breakage at a later time. Spontaneous breakage, though a rare occurrence, is a more pronounced risk with the higher residual stresses of fully-tempered glass than the lesser residual stresses of heat-strengthened glass. Recently, there have been numerous reports of incidents of spontaneous breakage occurring in single fully-tempered glass pieces installed overhead in vehicle sunroofs which have highlighted the potential risk of the phenomenon in all heat-treated glass applications. Regardless of the cause of breakage, the resulting release of internal residual stress causes fracturing of the heat-treated glass sheet into unbound glass particles.
Several methods have been pursued to modify single heat-treated glass pieces to limit the danger posed by the release of residual stress into unbound particles. Colored silicone, for example, has been sprayed onto the indoor face of single pieces as an opacifier for spandrel applications which also serves as a pliable structural backing for “fallout resistance” in the event of breakage. However, a sprayed polymer with pristine optical clarity for a vision application, hardiness for open exposure to the environment, as well as repellent of soiling has proved elusive. Another method is the addition of a polymer safety film to one or both faces of single heat-treated pieces. However applied films are vulnerable to degradation from the environment, including yellowing, scratching, peeling, or abrasions and add expense not just for initial installation but also field maintenance. A third method is the application of a polymer sheet to the face of the heat-treated piece which is adhered through compression and heat by means of a sacrificial cover sheet. However the exposed face of the polymer sheet is also vulnerable to environmental damage and even tiny specks of dust adjoining the sacrificial layer during processing produce blisters in the polymer surface and poor optical quality.
There is an ongoing industry effort to transition away from the installation of single sheets of fully-tempered safety glass in locations directly overhead, where the unsecured release of energy within the glass may result in disintegration and the release of falling glass particles, presenting a safety hazard. For example, following a well publicized incidence of fully-tempered glass panels spontaneously breaking on balconies in a high-rise building in Canada, Supplementary Standard SB-13 to the 2006 Ontario Building Code was enacted requiring measures be taken in the design of glass guards to reduce the probability of injury from falling, broken glass. More recently, the 2015 International Building Code now being adopted by local jurisdictions in the United States of America requires glass “used in a handrail, guardrail or a guard section” be a “laminated glass constructed of fully-tempered or heat-strengthened glass”. In the latter building code, traditional single pieces of fully-tempered safety glass are limited to applications “where there is no walking surface beneath them or the walking surface is permanently protected from the risk of falling glass”. In railing and many other glass applications, single, fully-tempered glass pieces are increasingly being transitioned to a laminated glass with two or more glass layers bound together by a plastic interlayer. This solution minimizes the risk of injury by unbound glass fragments in the event of breakage.
Laminated, bent safety glass consists of two or more sheets of annealed, or chemically-strengthened, or fully-tempered or heat-strengthened glass that are permanently bonded together by a tough, plastic interlayer. Such products exhibit a layered, sandwiched appearance, including a plastic interlayer visible as a dull band in the approximate middle of the glass edge thickness. A laminated safety glass, like single layer, fully-tempered glass, can qualify by testing as a safety glazing material in architectural and interior applications, since the glass mass remains substantially unitary without large tears, shears, or openings though some smaller particles may dislodge. When broken, the fractured glass particles remain bound together by the plastic interlayer, and the resultant broken assembly is restrained by the support system, and is therefore less likely to cause injury.
Bent, laminated glass panels for architectural and interior applications are almost invariably assembled with glass layers of like kind and thickness. For example, two layers of 5.7 mm. thickness bent chemically-strengthened glass may be laminated together with a polymer interlayer. This symmetry of layers reduces the complexity of design and specification as well as production. With the latter approach there is an intentional effort to replicate the characteristics between glass layers in the final laminated assembly, including their dimensional tolerances and shape. However, this approach, which typically characterizes flat, laminated glass production where bullet resistance or blast resistance is not required, has distinct drawbacks in the production of bent laminated glass products, and their resulting characteristics.
Laminated, non-heat-treated bent safety glass consists of two or more sheets of annealed or chemically-strengthened glass that are permanently bonded together by a tough, plastic interlayer. The glass sheets are heated in matching sets to temperatures of about 620 degrees C., bent together in a hot plastic state, and then cooled slowly to prevent the buildup of residual stresses within the glass. The non-heat-treated glass layers in the set conform substantially to the shape of each other. As a final step, the glass layers are marked by temporary ink on the same corner before disassembly for cleaning. At this time the glass layers may undergo chemical-strengthening if required. The glass layers in the set are then reassembled, carefully realigning the ink markings so as to return each glass sheet to its exact same position in the original hot bent set, followed by lamination. Optical quality is excellent because each set of non-heat-treated glass is bent together as a single unitary body.
However, laminated, non-heat-treated, annealed bent glass lacks enhanced strength and, as a result, is vulnerable to cracking from both thermal stresses and mechanical weakness. Additionally, there may be slight misalignment in the edges of component annealed glass layers after lamination, which may require repolishing if installed with an exposed edge condition. Repolishing already curved glass is a laborious process and in combination with the dull interlayer in the center of the thickness, bent laminated annealed glass panels never attain the high level of monolithic gloss finish possible with machine polished, single heat-treated pieces. Most importantly however bent, laminated, annealed glass is without strength enhancement in the glass layers and is at increased risk for cracking under thermal or mechanical loading. Cracking may result from mechanical loads if, for example, the glass panel is subject to high winds, accidentally “knocked” on exposed perimeter edges, or especially if subject to the high localized forces of mounting hardware attached through perforations in the glass. Additionally, cracking may result from thermal loads if for example an exterior glass panel is subject to high levels of solar energy absorption as occur with darkly tinted, spandrel, and low-emissivity coated glass, especially with simultaneous conditions of partial shading across the panel.
Laminated, non-heat-treated, bent chemically-strengthened glass demonstrates thermal and mechanical strength. Laminated panels with two or more layers of bent float glass of a soda-lime silicate recipe, and which have been chemically-strengthened, have for a number of years been commercially available. The enhanced strength provided by the bent chemically-strengthened glass layers is superior to simple bent laminated annealed glass panels. However, bent glass panels must often be fabricated from raw glass sheets already sprayed at time of manufacture by the primary producer with a water-damage-resistant, scratch resistant, low-emissivity and/or a reflective coating. The exchange of ions during the chemical-strengthening process is effectively blocked by the coating on the glass surface, requiring pre-coated glass be eliminated if strengthening is to be realized across all surfaces. Furthermore, glass with ceramic-frit paint fired into the surface during bending not only blocks the strengthening in painted areas but may introduce salt bath contaminants. Finally, laminated, chemically-strengthened glass is relatively more expensive due to its slow rate of production.
Laminated bent glass panels composed of two or more layers of thin, chemically-strengthened glass have been suggested as an improved light-weight product, most notably for vehicular applications. However, all bent laminated glass panels assembled from layers of chemically-strengthened glass exhibit a weakness at the edges when compared to single, fully-tempered glass pieces. The compressive stress in chemically-strengthened glass generally extends to a depth less than 150 microns and is thus many times shallower than, for example, the approximately 2,480 to 3,100 micron depth of compressive stress in a 12.4 mm. thickness, fully-tempered glass sheet. As a result, exposed unprotected perimeter edges, as well as the edges of perforations including holes or notches, leave the panel vulnerable to cracking from accidental impact or mechanical forces at these locations especially if the high compression is lessened by chipping or abrasions or scratches. Additionally if the perimeter edges or perforations are in misalignment after lamination, then the manufacturer's choice is between leaving the product with reduced edge quality, and reworking the product where dimensional changes relieve compression with a concordant reduction in strength.
Some hybrid bent laminated glass assemblies have been proposed in prior art that are assembled with different kind glass layers. For example, a thin annealed glass layer may be laminated to a thin layer of chemically-strengthened glass. However, such proposals have concentrated on automotive glazing and attaining high impact resistance to flying objects like hail and stones as well as mechanical strength suitable to attain ultrathin overall laminated panel assemblies that reduce vehicle weight and increase overall fuel economy. However, panel lightness and ultrathin assemblies are of limited utility in most architectural and interior glazing applications. While these properties may be desirable in their own right, single, fully-tempered glass pieces installed in architectural and interior applications have for many decades performed adequately in regards to their resistance to external impact, overall thickness, and weight. Where single pieces of fully-tempered glass have been inadequate for architectural and interior glazing is in the event of breakage, when the very residual stress providing enhanced strength results in an explosive detonation of the sheet, its disintegration, and the ejection of particles. Where the characteristics of a fully-tempered glass are desirable but the potential unbridled release of energy is considered unacceptable, the accepted solution within the bent glass industry has been to laminate together two or more layers of fully-tempered glass.
Laminated, heat-treated, bent safety glass consists of two or more sheets of heat-treated glass, fully-tempered or heat-strengthened, which are permanently bonded together by a tough, substantially translucent plastic interlayer. Breakage results in cracking, but fragments are bound together by the resilient, plastic interlayer, though some smaller particles may dislodge with the explosive release of residual stress in the event of breakage. Such glass exhibits enhanced strength compared to laminated, non-heat-treated, bent glass, especially in response to irregularities such as holes or notches. The strength of laminated heat-treated, fully-tempered bent glass is roughly four times greater than that of a laminated, non-heat-treated annealed bent glass of the same thickness. The strength of a laminated heat-treated, heat-strengthened bent glass is roughly two times greater than that of laminated non-heat-treated annealed bent glass of the same thickness. In both cases with heat-treated glass, the compressive stresses are deep, extending in a quarter to a fifth of the thickness of the glass from each major surface and this distance or greater from perimeter edges and perforations such as holes or notches. While these regions remain vulnerable to accidental impact or mechanical forces in all glass, the compressive stresses are deeper and more readily able to resist breakage when compared to bent laminated chemically-strengthened glass. However, the shape conformance of and between heat-treated glass layers is less accurate than non-heat-treated glass layers because the deep compression/tension forces always slightly alter the shape with some level of unpredictability.
Even with laminated, heat-treated, bent safety glass products there have hitherto been known disadvantages. The variable plastic interlayer thickness caused by poor shape matching between the sets of bent, heat-treated sheets produces optical waviness when looking through the glass. Another disadvantage is that edge quality may be very poor. Again, the plastic interlayer is visible as a dull band in the approximate middle of the glass thickness. Even with careful efforts to align heat-treated layers, unpredictable differences in shape conformance produce variations in sizing and nesting, often resulting in overhangs along the edges between one glass layer and another. Additionally, any polishing or dimensional change, once the bent glass is heat-treated, may cause breakage or later instability and therefore is prohibited. Tolerances listed in US industry standard ASTM C 1172 allow for a mismatch between assembled glass layers on the edges of laminated, heat-treated flat glass panels of as large as between 5.6 mm. and 7.9 mm. depending on overall assembly thickness. However the quality of edges is often found less than desirable in exposed edge installations when assembled in accordance with such standards. In addition, the wide range of tolerances leads to decreased edge quality at perimeters and perforations, which is further exasperated by shape requirements. One of our design goals is to remedy the latter problems and seek a more exacting solution.
Conventional bent, laminated, fully-tempered glass panels when used as a safety glazing material in architectural and interior applications typically exhibit imperfections along perimeter edges and perforations, such as holes or notches with misalignment and obtrusive overhangs. A conventional bent, laminated, fully-tempered glass panel also exhibits higher levels of transmissive distortion because of dissimilar symmetry between adjoining sheets. Irregular polymer interlayer thicknesses required to fill gaps between laminates are likely to produce unwanted optical distortion. Indeed, variations in the thickness of the plastic interlayer across local areas of the panel may result in a lens effect, where objects look larger or smaller when looking through the glass at varying angles and locations. Often such optical irregularities, as well as the visibility of the interlayer along the thickness, are compounded by the use of a thicker polymer interlayer that is better able to fill voids between mismatched layers. Conventional bent, laminated fully-tempered glass panels are inefficient to produce, with the repetitive fabrication of individual bent fully-tempered glass sheets and the potential risk of costly delamination resulting from the application of high forces that are needed to unitize the laminated assembly. In short, the problem is that it is virtually impossible to economically manufacture two identically matching, thick, bent and heat-treated glass sheets for lamination.
Known methods of manufacturing heat-treated, bent glass sheets through current bending technology are generally incapable of producing consistently matching, individual heat-treated glass pieces suitable for lamination using normal cost-effective methods. Compression/tension forces induced in the heat-treating process always slightly alter sheet shapes. Many production variables experienced during production influence product quality. Varying humidity and temperature of cooling air, production sequence, and tooling tolerances are factors. Further, differential heating patterns for glass, especially glass with a low-emissivity coating or ceramic-frit paint applied to all or part of the surface, slightly alter the distribution of residual stress and shape. Conventional industry equipment is designed for flexibility in shape and size, rather than sequential production of identical parts to exacting tolerances. Current laminating methodologies often result in the mechanical forcing of mismatched plies together. The lack of consistent matching of bent, heat-treated plies during lamination may cause optical distortion in the end product due to variable thicknesses of the plastic interlayer. Resultant edge quality is poor as bent, heat-treated glass plies may not be altered after production, and thus size differences or misalignment at the edges cannot be remedied with current technology. An inconsistency in matching enhances the visibility of the interlayer located in the glass center. Further, there is a risk of delamination caused by the forcing of dissimilar, heat-treated glass plies into a unitary laminated body.
The prior art reflects a wide variety of laminated glass products involving one or more of the above-discussed concepts. For example, U.S. Pat. No. 4,824,722 issued Apr. 25, 1989 discloses a safety glass laminate comprising a first sheet of organic or inorganic glass and a second rigid sheet, which may also be of organic or inorganic glass, with a flexible plastic interlayer therebetween that is bonded to each of the sheets by adhesive which has been cured by irradiation. The interlayer comprises two outer layers of plastic film and an inner layer of fabric, preferably woven polyester, interposed therebetween. The laminate may be employed as decorative cladding or as a panel for a glass door.
U.S. Pat. No. 5,496,640 issued Mar. 5, 1996 discloses fire resistant transparent, laminates comprising at least two parallel sheets of transparent material, at least one optically transparent fluorocarbon polymer, at least one optically transparent glass or resinous inner layer between the parallel sheets, and at least one layer of an optically transparent, intumescent gel.
U.S. Pat. No. 5,928,793 issued Jul. 27, 1999 discloses a laminated glass for vehicles comprising at least two single glass sheets which are laminated through at least one interlayer, wherein an outermost single glass sheet in a laminate comprising at least two single glass sheets is an alkali-aluminosilicate glass containing lithia. The laminated glass is suitable as the countermeasure of flying stones when applied to windows of vehicles. The alkali-aluminosilicate glass sheet is preferably obtained by a float method, and it is also preferably chemically tempered by ion-exchange.
U.S. Pat. No. 6,479,155 issued Nov. 12, 2002 discloses another fire-resistant, laminated glass panel. The glass-ceramic pane is joined, on each of its two faces, to a silicate glass pane by means of transparent, intermediate layers having a refractive index corresponding to the refractive index of the glass and the glass-ceramic. Transparent intermediate plies consist of a thermoplastic polymer having a high splinter fixation effect, and the silicate glass panes consist of tempered float glass.
U.S. Pat. No. 7,678,441 issued Mar. 16, 2010 discloses thermoplastic interlayer sheets or films for laminated safety glass with superior vacuum de-airing at elevated temperatures and superior tacking and edge sealing properties. The sheeting has an embossed surface pattern on at least one of the surfaces, which provides relatively uninterrupted channels for de-airing in at least two non-parallel directions.
U.S. Pat. Publication No. 2005/0276990 published Dec. 15, 2005 discloses a process for producing alumina coating composed mainly of alpha-type crystal structure, laminate coating including the alumina coating, a member clad with the alumina coating or laminate coating, and a process for production.
U.S. Pat. Publication No. 2009/0047509, published Feb. 19, 2009, discloses a coated glass pane with a low-e and/or solar control coating comprising at least a lower anti-reflection layer, an IR-reflecting layer, and an upper anti-reflection layer. At least one of the anti-reflection layers comprises at least one compound layer containing a mixture of an (oxy) nitride of Si and/or Al and of ZnO. The coated glass panes are heat-treatable, i.e., toughened and/or bendable.
U.S. Pat. Publication No. 2012/0028015 published Feb. 2, 2012 discloses laminated, transparent panes made of brittle materials and interleaved laminated films, wherein the brittle materials are various glasses, special glasses, glass-ceramics, transparent ceramics and crystalline materials. A process for producing and bending the panes and films, and its use thereof as bulletproof, unbreakable and shockproof glazing with a low weight per unit volume are disclosed.
U.S. Pat. Publication No. 2012/0328843 published Dec. 27, 2012 discloses thin laminated glass panels for vehicular applications with an external glass having a thickness less than or equal to 1 mm. and a non-chemically-strengthened glass sheet less than or equal to 2.5 mm. The disclosure highlights a laminated panel which claims superior impact resistance in response to impact events external to a vehicle, yet appropriately dissipates energy and appropriately fractures in response to impact event from the interior of the vehicle.
U.S. Pat. Publication No. 2013/0127202 published May 23, 2013 discloses glass laminates comprising at least one layer of strengthened glass having a first surface and a second surface disposed opposite the first surface, and one or more coatings adhered to the first surface of the strengthened glass, wherein the one or more coatings impart an asymmetric impact resistance to the glass laminate.
U.S. Pat. Publication No. 2013/0209751 published Aug. 15, 2013 discloses an alkali-aluminosilicate glass for 3D precision molding and thermal bending. The glass has a working point lower than 1200 degrees C. and a transition temperature lower than 610 degrees C.
U.S. Pat. Publication No. 2013/0295357 published Nov. 7, 2013 discloses a glass laminate with a chemically-strengthened, inner glass sheet with a thickness of 0.5 mm. to 1.5 mm. laminated to a non-chemically strengthened external glass sheet (annealed) with a thickness ranging from about 1.5 mm. to about 3.0 mm. The thicknesses of the sheets within the laminated assembly are of exemplary thinness to provide superior resistance to impacts and a reduction of weight for vehicular glazing with drawings of a curved glass embodiment illustrating a chemically-strengthened glass sheet that is larger in size than the non-chemically strengthened (annealed) glass sheet.
Pat. Application No. WO2014209861A1 published Dec. 31, 2014 discloses thin light-weight laminated glass panels with improved performance for vehicular applications resulting from an annealing process after ion-exchange. Laminated glass panels are disclosed in which at least one chemically-strengthened glass layer in the assembly has an enhanced depth of compressive stress of greater than about 60 microns to resist environmental damage as well as a reduced level of surface compressive stress between about 250 MPa. and about 350 MPa. for easier breakage if a vehicle occupant impacts the glass panel thereby reducing the risk of blunt force injury.
Pat. Application No. WO2015031594A2 published Mar. 5, 2015 discloses thin light-weight laminated glass panels with improved performance in external impact resistance, but with a controlled or preferential breakage behavior when impacted from the interior of the vehicle to minimize injury to the vehicle occupant. Laminated glass panels are disclosed with strengthened sheets having chemically-polished surfaces and a coating formed on one surface adjacent the interlayer to create a weakened surface. Additionally, a thin curved laminated glass panel is disclosed having a curved annealed glass sheet laminated to a chemically or thermally strengthened glass sheet which has been cold-formed to impart different compressive stresses for achieving a desired breakage behavior.
Despite the numerous prior attempts at perfecting heat-treated, bent glass laminates, the disadvantages or weaknesses associated with conventional glass panels are ubiquitous. A conventional bent, laminated fully-tempered glass panel provides the undesirable characteristic of poor quality on perimeter edges and perforations, such as holes or notches, with misalignment and obtrusive overhangs. A conventional bent laminated fully-tempered glass panel is typically characterized by higher levels of transmissive distortion with dissimilar symmetry between sheets, requiring an increased polymer interlayer thickness to fill gapping between bent glass sheets. The resulting irregular polymer interlayer thickness is likely to produce an undesirable lens effect and makes the dull plastic interlayer along the approximate centerline thickness even more visible. Production methods for conventional, bent laminated, fully-tempered glass panels are inefficient, requiring the repetitive fabrication of individual, bent fully-tempered, glass sheets and the potential risk of costly delamination resulting from the application of high forces to unitize the laminated assembly.
The avoidance of the above-mentioned difficulties is our design goal. Additionally, the high edge quality and enhanced strength of bent, single layer, fully-tempered glass is desirable but without the risk of particles dislodging and subsequent disintegration caused by the explosive release of internal residual stresses in the event of breakage including that which may occur spontaneously. The concurrent maintenance of desirable optical and aesthetic qualities, notably the avoidance of optical distortion and lens effects, as well as the avoidance of obtrusive overhangs and interlayer visibility at perimeter edges and perforations, remain highly desirable. The creation of such an improved bent glass, heat-treated laminate is the focus of our invention.